Periodic mesoporous organosilicas (PMOs) are organic-inorganic polymers with highly ordered pore networks and large internal surface areas. They were first reported in 1999 (Inagaki et al., Mesoporous Materials with a Uniform Distribution of Organic Groups and Inorganic Oxide in Their Frameworks, J. Am. Chem. Soc. 1999, 121.9611; Asef et al., Periodic mesoporous organosilicas with organic groups inside the channel walls, Nature 1999, 402, 867; Melde et al., Mesoporous Sieves with Unified Hybrid Inorganic/Organic Frameworks, Chem. Mater. 1999, 11, 3302). These organosilicas were synthesized using a surfactant template approach (Kreseg et al., Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism, Nature, 359, 710, 22 Oct. 1992. Burleigh et al.. Direct synthesis of periodic mesoporous organosilicas: Functional Incorporation by Co-Condensation with Organosilanes, J. Phys. Chem. B 2001, 105, 9935) and have narrow pore size distributions with few blocked pores or obstructions commonly found in amorphous materials to impede molecular diffusion throughout their pore networks. PMOs possess structural rigidity arising from the siloxane groups and functionality due to the organic bridging group. In addition. specificity can be imparted to the PMOs via a template directed molecular imprinting process. Due to their stnictural stability, functionality, and specificity, the PMOs are very efficient sorbents for the removal, sequestration, and pre-concentration of pollutants and/or any targeted compound from both vapor and aqueous phase. Yet a secondary means, such as a spectroscopic or electrochemical technique, is required for the specific detection of the sorbate. The addition/embedding of molecules (ie molecular catalysts) would in effect add a catalytic capability to PMOs through the activity of the embedded molecule upon excitation.
Periodic mesoporous organosilicas (PMOs) provide organic functionality in a silica matrix through the combination of covalently linked organic and silica components. Material characteristics can be tuned for a particular application by changing the organic groups used as “bridges” in the silica matrix. The organic-inorganic polymers lend stability, selectivity and ease of modification to applications traditionally protein- or microorganism-based. Template directed molecular imprinting, employing a target-like compound, can be used to improve pore homogeneity and distribution and to enhance selectivity and binding characteristics. The use of a regenerable diethylbenzene-bridged PMO for the preferential adsorption of hydrocarbons over time scales on the order of minutes has been demonstrated previously. Other applications of PMOs include catalysis, filtration and/or purification, and chemical sensors. Decontamination applications involving PMO materials are based on adsorption of the contaminant onto the silicate, and not on degradation of the contaminant.
A porphyrin is a nearly flat molecule with a macrocycle of twenty carbon and four nitrogen atoms consisting of four pyrrole rings joined by methine bridges. The porphyrin macrocycle binds cyclic compounds cofacially even when the compound bears a nitrogen or the porphyrin has a metal coordinated to the central nitrogen atoms. They have been used as catalysts in a wide range of applications: degradation of chlorinated phenols, nitro-substituted toluene, and atrazine; oxidation of alkylaromatics; and oxidative cleavage of C—C bonds. When compared to proteins and microorganisms, porphyrins and metalloporphyrins are much less sensitive to variations in conditions such as temperature and pH than proteins and microorganisms and have been shown to withstanding temperatures above 150° C. The binding and catalytic characteristic of porphyrins can be altered through modification of the peripheral substituent groups or through incorporation of metals via coordination to the four central nitrogen atoms.
The molecular structure of the porphyrin consists of a large macrocycle around which a minimum of 22 π-electrons are shared. This large number of π-electrons results in a large extinction coefficient and spectral characteristics that are highly sensitive to changes in the environment of the molecule. Recent work (White, et al., Reagent-less detection of a competitive inhibitor of immobilized acetylcholinesterase, BiosenBioelec 2002, 17, 361, incorporated herein by reference) has shown that porphyrins can be used in conjunction with enzymes to achieve a higher degree of selectivity and allow for specific detection within a class of compounds only. The reversible, competitive inhibition of an enzyme by a porphyrin has been used for the detection, both in solution and vapor phase, of analytes such as organophosphates (including nerve agents/simulants) and carbon dioxide (White, et al., Enzyme-based detection of Sarin (GB) using planar waveguide absorbance spectroscopy, SensLett 2005, 3, 36 and White, et al., Competitive Inhibition of Cabonic Anhydrase by Water Soluble Porphyrins: Use of cabonic anhydrase as a CO2Sensor. SensLett 2005. 3, 59, both incorporated herein by reference).
The most well known example of porphyrin photocatalysis is photosynthesis in which the porphyrin is the central part of chlorophyll. Porphyrins have also been used as synthetic photocatalysts and are well know for generating reactive oxygen and nitrogen species. Porphyrin production of perioxides has also been demonstrated and this peroxide has been implicated in a Fenton-like cycle for the degradation of aromatic compounds. Evidence indicates the involvement of multiple pathways for the photocatalyzed degradation of aromatics by porphyrins including those involving activated water, reactive oxygen species, peroxides, and direct energy transfer.